1. Field of the Invention
The present invention relates to target detection using active optical sensing techniques and, more particularly, is directed to a two channel active optical object sensor that takes advantage of the reflective characteristics of the object being detected as compared to the reflective characteristics of other background objects in the surrounding area.
2. Description of the Prior Art
Discriminating targets or object surfaces from their surrounding environment is an outstanding problem in a number of applications. In one application, for example, fuzes have been designed which attempt to discriminate between foliage and targets which hide under the foliage umbrella so that projectiles and missiles or the like do not prefunction on the foliage on their way to the target. So far no satisfactory solution has been found which does not require two completely separate sensing techniques such as those that use both optical and magnetic sensors. The problem is a critical one for a fuze which must provide a few meters stand-off for an anit-tank shaped charge, where the missile or projectile may pass near or through foliage on its way to the target.
Fuzes have existed for a long time that use active optical sensors. Until recently the primary focus of attention has been target discrimination in an aerosol environment where the backscattered returns are in general of very low amplitude with large pulse stretching. See, for example, U.S. Pat. No. 4,709,142 directed to target detection in aerosols using active optical sensors by Dahl. The discrimination has been based on using multithreshold electronic firing logic and very short pulse widths. However, optical clutter from foliage has recently started receiving attention. The problems posed by this clutter are quite different from those posed by aerosols because of the expected high amplitude of the return signals along with large pulse stretching. Since leaves are usually distributed in layers, there are multiple reflections and transmissions of the incident radiation by the leaf layers to make up the reflected pulse. The reflected pulse received at the receiver has relatively high peak amplitude and considerable amount of pulse stretching due to reflections occurring at different distances. A target/foliage discrimination scheme based on pulse stretching for an electronic logic processor has marginal success, and such a scheme may not be applicable for some systems. Similar difficulties exist in differentiating between target and foliage returns for rf fuzes.
At the present time it does not appear possible to design a logic scheme which can handle a foliage clutter problem without designing another type of sensor with an additional input channel. The current techniques in use do not adequately detect target objects. Consequently, it is desirable to be able to have an apparatus that provides better object detection techniques that can detect target objects from their surroundings.